Final answer:
When large amounts of alcohol are present, it displaces air, leading to a lower reading of air content due to the high pressure to low pressure gas movement.
Step-by-step explanation:
When large amounts of alcohol are used, the direct reading will tend to indicate a lower air content. This is due to the fact that alcohol has a tendency to evaporate, thereby taking up space and displacing some of the air. In the context of gas laws and pressure, gas generally moves from an area of high pressure to an area of low pressure as demonstrated when considering how hot air balloons work.
The pressure of the gas inside the balloon must be greater than that of the surrounding atmosphere for the balloon to ascend.